IARC 60th Anniversary - 19-21 May 2026
Session : Environmental and occupational cancer: an underestimated burden?
Exposure to pesticides and the risk of breast cancer in an international consortium of agricultural cohorts (AGRICOH)
KIM J. 1, OHLANDER J. 2, RENIER M. 3, BALDI I. 4, BEANE FREEMAN L. 5, LEBAILLY P. 3, NORDBY K. 6, SCHÜZ J. 1, KROMHOUT H. 2
1 Environment and Lifestyle Epidemiology (ENV) Branch, IARC/WHO, Lyon, France; 2 Institute for Risk Assessment Sciences (IRAS), Utrecht University, Utrecht, Netherlands; 3 ANTICIPE, Centre de Lutte Contre le Cancer François Baclesse, Université de Caen Normandie, Caen, France; 4 EPICENE, Bordeaux Population Health Research Centre - INSERM U1219, Université de Bordeaux, Bordeaux, France; 5 Division of Cancer Epidemiology and Genetics, US National Cancer Institute (NCI/NIH), Bethesda, United States; 6 National Institute of Occupational Health (STAMI), Oslo, Norway
Background: The international consortium of agricultural cohorts (AGRICOH) was established jointly by IARC and NCI/NIH in order to examine associations between agricultural exposures and health outcomes, such as between pesticides and cancer.
Several pesticides have endocrine disrupting properties, but few studies have examined breast cancer risk in relation to specific active ingredients. Existing studies consider exposure from application or mixing (“use”), which is less common for female farmers, but none account for exposure from entering sprayed crops to carry out farming tasks (“re-entry”).
Objective: Building on previous work in AGRICOH, we aimed to: a) assess exposure to additional pesticides (71 in total) from both use and re-entry, and add metrics of probability, intensity, and frequency; and b) to investigate the associated risks of breast cancer, overall and by menopausal status.
Methods: We used data from three cohorts: the French Agriculture and Cancer Cohort (AGRICAN, 2005-2017), the US Agricultural Health Study (AHS, 1993-2021), and Cancer in the Norwegian Agricultural Population (CNAP, 1993-2024). Lifetime exposure to specific active ingredients was estimated from crop-exposure matrices (CEM), self-report, or both. Cohort-specific adjusted hazard ratios (HRs) and 95% confidence intervals (CIs) for breast cancer were estimated using Cox regression and combined using random effects meta-analysis.
Results: During the follow-up period, 9422 cases of incident breast cancer occurred in the combined population of 161,000 female farmers and farmers’ wives. Extensive additional exposure assessment work was undertaken in the AGRICAN and CNAP cohorts. Among the active ingredients examined so far, the median numbers of exposed cases were 21 (IQR: 11-30) in AGRICAN and 51 (IQR: 30-91) in AHS. The most commonly used pesticides in AGRICAN were diazinon and parathion, and in AHS, carbaryl, glyphosate, and malathion were the most common. In preliminary analyses of 31 active ingredients assessed in both AGRICAN and AHS, no clear evidence of an increased risk of breast cancer was observed for ever use of a specific active ingredient. Additional results including CNAP and accounting for re-entry exposure will be presented.
Conclusion: This is the largest prospective analysis of specific pesticide active ingredients and breast cancer risk. Strengths include assessment of re-entry and probability of exposure, reducing misclassification, and additional study power from meta-analysis. Cohort heterogeneity presented challenges. Our findings will be relevant to future evaluations of the carcinogenicity of pesticides.